BIG PHYSICS, BIG QUESTIONS –

Lasers slim down on stopped-light diet

A new kind of laser that powers up by freezing light in its tracks could lead to computers that run on photons instead of electrons.

Researchers already have ways to slow light down and even stop it completely for as long as a minute.

Now Ortwin Hess at Imperial College London and his colleagues say that this principle could be used to shrink lasers. Ordinary lasers work by bouncing light between two mirrors, so photons of a certain wavelength accumulate. But these devices can’t be made very small. A stopped-light laser would be different, says Hess.

The laser consists of an electrically insulating material sandwiched between two metals. Pulses of light travelling in one direction through the insulator reverse direction as they enter the metal, trapping the light in a vortex. “It’s like if you walk up a hill made from sand, every step you take forward, the sand takes you a step backwards,” says Hess.

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Simulations show that energy builds up in the vortex for around 10 trillionths of a second before it breaks free in a coherent beam of light, just like a laser. What’s more, it could potentially release a range of frequencies at once, more like a light bulb than a traditional laser with a characteristic colour.

The team is now working to build the laser, says Hess. If they succeed, it could find a use in optical computing, where information is transported by photons rather than electrons. Other lasers are too bulky for nanoscale circuits, but a stopped-light laser would be small enough, enabling faster data transmission within a chip.